Carb. for a 383 9.8 to 1 compression.

[blue69runner]

So my motor will run pretty good with a Holley 650 carb I have. Crazy it runs fine for a while then wants to act up. Was running too rich with primary jets at 80 and changed back to 76 jets. Was getting spark knock at cruz speed about 65 MPH. This thing has been going from one end to another. Have tired fuel boost. Now running a mix of 93 non ethanol about two gallons added to a tank of 93 ethanol base fuel. Talked to my motor builder and he told me I need a larger CFM carb like a 750 for my motor. Like stated 383 with 9.8 to 1 compression. Half dome pistons. Stock heads and stock manifolds. Running the Orange box. Wonder if that is not my problem. About 3000 miles on the motor since rebuilding it. After changing the jets back to 76's at about 65 hit the gas and kicked in the four barrel it popped a couple of times then took off. Guess I have something wrong. Any input will be greatly appreciated. Blue.

 

[YY1]

What cam?

I had a heck of a time tuning a carb on my 9.5:1 383 with a DC 284/484 cam. Otherwise stock build.

Ended up with a 650 vac secondary with small jets/valve in front and plate with large valve in rear from a larger carb.

 

[Don Frelier]

I had an orange box that would misfire around 4,000 rpm or above. Tried everything and stuck in an old parts store replacement ECU and it ran perfect.

How about the rest of the fuel system? If its original take off the fuel filter and cut it in half maybe rust in there.

Finally fuel pump pushrod length?

Keep in mind that at 9.8:1 especially since you ran it rich for a while it's going to tend towards predetonation as the carbon builds up.
Mine was 9.4 and I could run it on 89 for a few years then I had to go to premium after about 10,000 miles.

Sorry I can't help with a Holley

 

[dvw]

Theres way more to carb tuning than just jets. Tip in pop is lean. But not necesarily jetting. Could be accelertor pump nozzels, pump cam, or secondaries opening to quick if it's not a double pumper. My 372" small bloock runs fine with a Holley 650 double pump. Is it to small? Maybe, but it's a mild 9-1 motor that has run 12.50@110 at 3750lbs. Been awhile but as I remember it's jetted around 68/74.
Learn here: Holley accelerator pumps/cams
Doug

 

[blue69runner]

Thank you for all the info. Food for thought for sure. Changing my plugs once again to the right heat range plug. This could be my problem also. Have been told to change my orange box to chrome box. Going to do that also and see if it is my box. Don't know if the blast resistor will need to be changed also. Seems like where never done working on these old cars. LOL.

 

[lewtot184]

why would somebody put 80's in a 650? then again why would somebody put 76's in a 650? has the power valve(s) been removed? look up the list number on the carb and base line the jetting from there. no telling how much crude and fouling is in the combustion chamber and plugs from crummy jetting.

 

[66Satellite47]

Lot s of work in really tuning a carb. I've always been a Holley guy so I learned how to tune them based on how they are designed. With my 440 drag car I spent a several weeks and many runs trying to optimize my 850DP. The main jets were pretty easy. Not too much different than stock Holley. The accelerator pump took a litter more, shooter size, shooter cam size/shape. I eventually bent the arm to work with the acc cam I chose. Lots of work but it sure worked out. My point is learn how a Holley carb works and what you need to work on. Power valves and jet size need to be properly matched.
Edit: I have never been a fan of the Mopar Orange box, but be careful which Chrome box you go to.
Edit 2: The color of an aftermarket ECU means nothing, The color of the original Mopar ECU's meant something, but you still had to be careful.

 

[dvw]

Thank you for all the info. Food for thought for sure. Changing my plugs once again to the right heat range plug. This could be my problem also. Have been told to change my orange box to chrome box. Going to do that also and see if it is my box. Don't know if the blast resistor will need to be changed also. Seems like where never done working on these old cars. LOL.

Depending on list number the stock jetting is;

4777 650cfm
Primary Main Jets 71
Secondary Main Jets 76
Power Valve 6.5
Primary Sq. Nozzle .025
Secondary Sq. Nozzle .025

4777 (-1 -2) 650cfm
Primary Main Jets 67
Secondary Main Jets 76
Power Valve 6.5
Primary Sq. Nozzle .028
Secondary Sq. Nozzle .028

4777 (-3 -4 -5 -6 -7) 650cfm
Primary Main Jets 67
Secondary Main Jets 73
Power Valve 6.5
Primary Sq. Nozzle .028
Secondary Sq. Nozzle .028

 

[blue69runner]

The secondary plate is an 80 jet fixed. So it had 76 on the primary jets. When I got the carb on the car. There is no numbers on the carb it is an early Barry Grant carb. After talking to Holley said that is what I have. Running a 6.5 power valve new. I had squared the front jet to match the metering plate on secondary. Was running too rich. So now backed down to 76 jets primary. Putting in new plugs and going to take a reading after taking it for a drive. Did the math on 383 and it is the right size carb for my motor. My motor guy says I need a 750 cfm carb. I don't know why he would say that if the numbers say I need a 650 cfm. Well the car was running fine then started to act up. Was getting spark knock when at Cruz speed. Some bucking when letting off the accelerator. So like most mopar's have to find the sweet spot or most motor. Thanks again for the info just have to get it fined tuned. Blue.

 

[66Satellite47]

If you have one of the Holley 650's that used a plate style secondary, tuning gets a bit more complicated. They had a lot of combinations they put out there. An 80 plate sounds pretty big for a 650 carb. If it's a Barry Grant carb, no idea what you have there.

Edit: I may have been confused, the wide variety of Holley's with secondary plates were 600's maybe a few 650's. The specs that dvw posted are for a double pumper which with the right tuning could work well on a mild 383.

 

[SlinktRR]

650cfm is fine but maybe too much jetting and fouled plugs. What is your idle vacuum, what cam. Are you running vacuum advance. I run larger secondary jets than primary for street with a power valve dictated by vacuum but those jet numbers sound too much for a mild 383.

 

[YY1]

The secondary plate is an 80 jet fixed. So it had 76 on the primary jets. When I got the carb on the car. There is no numbers on the carb it is an early Barry Grant carb. After talking to Holley said that is what I have. Running a 6.5 power valve new. I had squared the front jet to match the metering plate on secondary. Was running too rich. So now backed down to 76 jets primary. Putting in new plugs and going to take a reading after taking it for a drive. Did the math on 383 and it is the right size carb for my motor. My motor guy says I need a 750 cfm carb. I don't know why he would say that if the numbers say I need a 650 cfm. Well the car was running fine then started to act up. Was getting spark knock when at Cruz speed. Some bucking when letting off the accelerator. So like most mopar's have to find the sweet spot or most motor. Thanks again for the info just have to get it fined tuned. Blue.

That explains why I had to change the plate on my secondary side.

The issue my engine had was that it wanted a lot of "signal" and not too much fuel on the primary side but it wanted quite a bit of fuel when the secondaries opened.

Once that clicked, and I put all the parts together, it ran great.

I always refereed to that as "frankencarb" after that.

 

[rumblefish360]

Replace the metering plate with a plate that will use jets.
Much more effective and takes up zero room or I should say, it doesn’t make the carb longer/larger in size.

 

[dvw]

If you have a plate I don;t believe it's 650. What's the list number on the choke horn? Also from experience 9.8-1 with factory heads and a small cam is going to be very detonation sensitive. Chances are you can't put enough timing in it on pump gas.
Doug

 

[blue69runner]

Crane thumper cam. Open plane Holley mid-rise intake. No numbers on the carb. horn. But Holley assures me it is a 650 carb. Ran a vacuum check and running a 6.5 power valve. Funny it run's ok then gives me trouble. We all know trying to find the sweet spot is trying sometime. So will keep tinkering with it. Now have the blue box ECM coming. We all know about these aftermarket parts. Have the right heat range plugs and changing them out now. So, time will tell what the problem is. Got a lot of info now to decide which way to go. If the carb does not work out going to get a 750 cfm and put that on it. If this dose not get it then getting a dual plane intake and try that. Ok appreciate all the info and will be back at you guys with what I find is my problem. Thanks Blue.

 

[dvw]

Crane thumper cam. Open plane Holley mid-rise intake. No numbers on the carb. horn. But Holley assures me it is a 650 carb. Ran a vacuum check and running a 6.5 power valve. Funny it run's ok then gives me trouble. We all know trying to find the sweet spot is trying sometime. So will keep tinkering with it. Now have the blue box ECM coming. We all know about these aftermarket parts. Have the right heat range plugs and changing them out now. So, time will tell what the problem is. Got a lot of info now to decide which way to go. If the carb does not work out going to get a 750 cfm and put that on it. If this dose not get it then getting a dual plane intake and try that. Ok appreciate all the info and will be back at you guys with what I find is my problem. Thanks Blue.

Instead of throwing parts at it take a step back. Look at what is happening. If it's ignition you certainly won't fix it by switching the carb. Look here;
How to Identify Your Holley or Demon Carburetor.

 

[SlinktRR]

If you can still find the rev n nator I would use that. It's a really nice ignition box I use it and their coil. The chrome box is my back up and it's very nice as well.

 

[Geoff 2]

Good carbs like Carter, Edel run ok all of the time, not some of the time....

 

[OzCharger69]

I run a Holley Street Avenger 770 on the same setup with great success

 

[69hemibeep]

In your first post you mentioned half domed pistons which makes me question the compression ratio. How far down on the hole are they at TDC what pistons and heads are they, (stock heads came in several camber sizes) have the heads been milled and what head gasket?